Bunn et al. [2005] – 20th century tree growth in the Sierra Nevadas

Bunn et al. [2005] have an interesting discussion of 20th century tree growth (especially foxtail pines) in the Sierra Nevada and White Mountains, in the current Holocene, which, needless to say, was interesting to me. The extraordinary and uncritical embedding of MBH98-99 in paleoclimate mentality recurs here in a curious way. Roger Pielke wondered whether the emphasis on deconstructing the hockeystick is warranted in policy terms ( a question that I mean to discuss some time); here is a case where the embedding of the hockeystick leads to problems in a scientific paper relying on Mann et al., without fully understanding its assumptions and defects.

Bunn et al. report on a network consisting of 13 tree ring site – 7 collected by co-author Graumlich and her students (including Bunn), 6 are Graybill series archived at WDCP. The Graybill series include some familiar sites to readers of this site: Sheep Mountain and Campito Mountain (both bristlecones) and 4 foxtails. The 6 sites include the strongest hockey stick shaped sites in the MBH98 NOAMER roster. Although the Bunn et al. network overlaps the MBH98 network, they describe it as significantly augmenting" the network.

Our 13 sites and five species significantly augment the existing North American tree-ring proxy indicator series (Mann et al., 1998, 1999) in two ways that enhance the interpretation of the record. First, our high elevation chronologies include three species not represented in previous work. In addition to foxtail pine (Pinus balfouriana) and bristlecone pine (P. longaeva) we contributed western juniper (Juniperus occidentalis), limber pine (P. flexilis) and whitebark pine (P. albicaulis).

Here is a listing of the Bunn et al. [2005] sites. The 7 new sites differ from sites reported in other articles by the authors, but no explanation is given as to the selection here.

Code

Site

Species

Altitude

Lat

Long

Strip-Bark

SL

Spillway Lake

PIAL

3305

37 50

119 13

N

MP

Mammoth Peak

PIAL

3350

37 52

119 17

N

BP

Boreal Plateau

PIBA

3420

36 27

118 20

N

UWL

Upper Wright Lakes

PIBA

3510

36 37

118 22

N

HAM

Hamilton

JUOC

2630

36 34

118 39

N

CRA

Crabtree

PIBA

3378

36 34

118 22

N

LU

Lundy Lake

PIFL

2925

38 3

119 14

Y

MBH98-99

CIR

Cirque Peak

PIBA

3505

36 27

118 13

N

FLO

Flower Lake

PIBA

3291

36 46

118 22

Y

SHP

Sheep Mountain

PILO

3475

37 22

118 13

Y

CAM

Campito Mountain

PILO

3400

37 30

118 13

Y

TGL

Timber Gap (Upper)

PIBA

3216

36 22

118 37

Y

TGU

Timber Gap (Lower)

PIBA

3017

36 22

118 37

Y

The above comments have to be taken with a grain of salt. There are actually 8 JUOC and 8 PIFL sites in MBH98 (although none in the 1000-1399 MBH99 addition). It’s hard to see how the PIAL sites (SL and MP in the first row below) show anything unique about the 20th century – so the addition of these sites and this species is simply window-dressing. The juniper site (HAM) is unambiguously precipitation-controlled. It shows an uptick during the 20th century; Knapp et al. [2001], cited by Bunn et al., argued that higher CO2 levels increased water use efficiency in junipers – so this would not seem to be independent evidence of climatic change. An earlier work by Bunn et al. [Bunn et al, 2003] had argued that higher CO2 levels also improved water use efficiency in strip-bark forms. The new PIFL site (Lundy Lake) is strip-bark – so again this is not new unambiguous evidence (20th century levels are similar to MWP levels anyway at this site.) However, there remain 3 new foxtail sites (BP, UWL, CRA) which are not strip-bark (also Cirque Peak is a Graybill foxtail site, which is shown as not strip-bark.)

Figure 1. Figure 2 from Bunn et al. [2005].

Graumlich [1991] was an earlier discussion of foxtails by one of the co-authors, which has itself been widely cited in discussions of CO2 fertilization. The sites reported in Graumlich [1991] were also foxtail sites from the same area (See below). One (Crabtree) appears to overlap directly; Upper Wright Lakes site (36o37;118o22,3510) is obviously very close to the previous Bighorn Plateau site; the previous Boreal Plateau (36o27; 118o20, 3420) is a little SW of Crabtree.

Code

Site

Species

Lat

Long

Altitude

WTF

West Tyndall F

PIBA

36 39

118 23

3450

WTL

West Tyndall L

PIBA

36 39

118 23

3450

BP

Bighorn Plateau

PIBA

36 36

118 22

3430

CR

Crabtree

PIBA

36 35

118 22

3350

KP

Kaiser Pass

JUOC

37 17

119 5

2700

The tree-ring chronologies in the earlier study did not have enhanced 20th century growth, as shown in the former Figure 2. In fact, the absence of enhanced 20th century growth in the sites studied by Graumlich [1991] was considered by her to be strong evidence against the hypothesis of CO2 fertilization.

These previous arguments are not re-visited and reconciled in Bunn et al. [2005]. Now for the connections to MBH98. Bunn et al. state:

The possibility that tree growth (e.g., annual rings) in natural environments has been fertilized by elevated atmospheric CO2 in the last several decades of the twentieth century has been discussed in several dendroecological studies (e.g., LaMarche et al., 1984; Graumlich, 1991; Briffa, 1992; Graybill and Idso, 1993; Nicolussi et al., 1995; Knapp et al., 2001). … There is no consensus, however, on the presence or impact of CO2 on growth; a review article on the subject states that there is inconclusive evidence to support CO2 enhancement on tree growth in natural environments (Jacoby and D’Arrigo, 1997). Given the potential for multiple interpretation of the growth signal in this data set, however, we feel compelled to address this issue further.

This is not a very imposing survey of recent literature on the impact of CO2 on high-altitude growth. They don’t mention the important studies from Kàƒ⵲ner or Hattenschwiler or the many FACE (free air CO2-enhanced) studies. Jacoby and d’Arrigo can hardly be considered unbiased.

They go on to say:

The dramatic trend that is seen in the late twentieth-century growth rates of the trees in this study is similar to that seen in other palaeoclimate research, particularly the Mann-/Bradley-Hughes (MBH) multiproxy reconstruction of Northern Hemisphere annual temperatures (Mann et al., 1999).

Notice the embedding: the MBH98 reconstruction on a millennial scale is NOT robust to the presence/absence of bristlecone/foxtails, so it is hardly surprising that a network which is dominated by foxtails/bristlecones should look like MBH98. They are not independent networks. Bunn et al. then discuss MBH98 as follows:

By combining instrumental temperature data with multiple temperature-sensitive proxy records, the MBH reconstruction indicates that the twentieth-century warming is abrupt and truly exceptional in the context of the last millennium. Because of concerns about CO2 fertilizations affecting the results of that reconstruction, the reconstruction was rebuilt with a sparser data set without tree-ring data (instead relying on historical instrumental, coral and ice-core records), and the authors verified that there was no bias from non-climatic influences on their tree-ring data sets (Mann et al., 2000).

This non-robustness claim of Mann et al. seems especially objectionable to me. The calculations in their CENSORED directory show that they were well aware that their 15th century reconstruction was not robust to the presence/absence of bristlecones. Without the bristlecones, there is no MBH98-99 evidence that 20th century warming is "abrupt and truly exceptional". If one wanted evidence for just how misleading the Mann et al. [2000] discussion of robustness is, the reliance by Bunn et al. right here is surely an example. Bunn et al. then say:

Comprised mostly of high-elevation tree-ring data, the MBH tree-ring data are similar to the data used in this study. As the MBH data show no evidence of CO2 fertilization in their high-elevation tree growth data, we have no reason to suspect that the growth trends seen in this work are related to atmospheric CO2 fertilization. Instead it is our contention that the signals seen in these data are the result of climatic influence.

The sleight-of-hand, relying on the misrepresentation by Mann et al., is completed. Mann et al. cannot argue anything about the 15th century or earlier without the bristlecones. So Bunn et al. cannot rely on MBH conclusions (using virtually the same sites) to show that their sites are climatic.

***…One-third of scientists surveyed said that within the previous three years, they’d engaged in at least one practice that would probably get them into trouble, the report said. Examples included circumventing minor aspects of rules for doing research on people and overlooking a colleague’s use of flawed data or questionable interpretation of data…

Nearly 13 percent of those who responded said they’d overlooked “others’ use of flawed data or questionable interpretation of data,” and nearly 16 percent said they had changed the design, methods or results of a study “in response to pressure from a funding source”…***

Yeah…the whole thing is circular. On the CO2 fertilization front, are you just raising that as a possible confounding factor or do you feel strongly that it is? Why don’t we have the story settled on this basic issue?

TCO, I think the issue is that the local instrumental records close to these Bristlecone/Foxtail sites show little 20th century temperature increase, yet at least some of the ring widths show significant growth spurts over the same time scale. Therefore the growth spurts are unlikely to represent a temperature increase as none has apparently occurred. Hence the interest in finding some other explanation, with precipitation, some form of dust fertilisation, or CO2 being the most immediately apparent. Graybill & Idso attributed the growth to CO2, but that could be because Idso at least is an expert/specialist in that area.

I just noticed that this article has some plots of the 2 foxtail sites used by Esper, otherwise unplished – Boreal Plateau and Upper Wright Lakes – both with pretty pronounced hockey stick shapes, whcih is not a surprise. But I’m sure that Esper’s shape will be provided by a few series, with the rest being cancelling noise.

On CO2 fertilization, IPCC 2AR said that CO2 fertilization was an issue possibly limiting applicability of tree rings. My point is that sites suspected of CO2-fertilization should not have been inserted through the back door.

The UWL series is a little curious: I wonder when it was done.

I’ve requested data from Graumlich without any success. Some of this data is 15 years old without being archived.

And my point is that we should figure out how the damn CO2 fertilization works. Is there at least a survey article that looks at all the previous studies? If not, that’s another pub to put on your work list. you should really throw in the towel and just get a job as a tree scientist. You’ve read so much of the damn literature. Don’t hide behind not understanding everything. nobody ever does, Steve. Maybe better if you did it at an American uni. Canada seems a little smaller and harder to find a spot if you don’t fit in with the Feds. US has just got more diversity.

I am not sure that anyone is following up on this thread… From what I gather this site is not supportive of Mann et al. which is fine to take issue with a particular technique if it has been used incorrectly – I won’t pretend to know the details of their calculations. As a tree-ring scientist and plant physiologist I am interested in all the facts from whatever source and will just put in my 2 cents for others to judge as they will.

First- there are numerous other peer-reviewed publications that have independently found warming-effects on biological/ecological systems throughout the globe – folks should not get so hung up on Mann et al., even if for some reason it was deficient in some manner.

The reality is that CO2 does indeed increase photosynthesis but it does not always increase plant growth proportionally. Growth and carbon partitioning within a plant is species specific (see Korner et al. 2005 in Science). Also- growth in high CO2 is much greater when trees are young. This sensitivity fades with age for reason I won’t get into now. Anyway, there may be some SMALL holes in the arguement for reconstructing temperature without accounting for CO2, but they are SMALL (because most of the tree-rings used are when the tree is quite old – especially over recent periods). In addition, most of the long-lived trees you might inspect are very temperature-limited and small increases in mean temp’s can have large affects on tree-ring growth – I have a paper in the works (Ecology) that should be coming out, hopefully, in the next year to try and sort out some of the issues due to CO2 fertilization and tree-rings.

Steve, thanks for the comment. Surely the arguement with MBH (and other studies) is the unfailing attribution of any warming to Anthropegenic causes. MBH is important as it has been used as the proof that the current climate is unique and hence a comfortable attribution of warming = AGW is made. What Steve M has helped to show is that the evidence that the current climate is unique is in fact not good, the data used by MB&H in both MBH98 & 99, and in all so far examined such paleoclimate studies (which is, BTW, not all such studies) does not necessarily support this conclusion.

At least some of the criticisms made of MBH, as I trust you will have gathered from this site, is based on MBH’s use of several tree ring records which are in fact essential for its “hockey stick” shape. One set of this data is broadly referred to as the “Bristlecones” although there is at least one other species included. The data from these sites was first published in a 1993 paper by Graybill & Idso, which concluded that although the ring widths were significantly wider in the 20th Century, that this was not related to temperature, from studying the local temperature records. This did not stop MBH using these records as temperature proxies. What is more, as SM’s researches have uncovered, there are some unusual features in this data set. Apparently trees with a “strip bark” form are particularly likely to have the largest width increases for example. The original paper suggested CO2 fertilisation as the cause of the wider rings, and other alternatives also exist, mineral fertilisation, grazing effects, precipitation, etc.

There is also the issue, discussed elsewhere on this site, that a species response to temperature is very possibly not a linear response. Although an increase can, as you put it “small increases in mean temp’s can have large affects on tree-ring growth”, a small increase could also lead to a decrease in growth, that is the response can be, for example, an ” inverted U” shaped curve, and this possibility has been entirely ignored by the paleo-climate community to date. Furthermore, some of the other prominent tree ring (and MXD) data series have significant data problems, the Polar Urals dataset falls into this category, the altitude data (obviously important) is poorly recorded. Other problems include the cherry picking of data (Gaspe Cedars for example), and other selection issues.

So, to end a long post, many here would disagree that ” there may be some SMALL holes in the arguement for reconstructing temperature without accounting for CO2, but they are SMALL “. Many unstated assumptions made in using tree ring & MXD data seem at least in part, untenable.

I for one are happy to see an expert in this field commenting here, and we look forward to further posts. I hope you get the chance to read more off this site and perhaps comment on some of the above and other issues. Steve M would, I feel sure, be more than happy to discuss the serious science matters with you, both online and offline.

Welcome to this blog. As Ed Snack indicated, there are many discussions here of various factors of tree growth which you might not yet have read, but your comments upon which may be of interest.

BTW, since there are several Steves in addition to our host who comment here, let me suggest that you add some letter to your signature, which need not be the first letter of your last name, to facilitate distinguishing comments to you from comments to other Steves.

These are Bristlecones practically on top of each other, yet showing much different growth reactions. The simplest explanation, IMHO, would be a LOCAL, non-temperature, even prb’ly non-climatic effect.

First, I don’t deny that there is evidence of 20th century warming. The question that interests me is the different one: how can the various multiproxy studies conclude that the late 20th century is warmer than all other periods in the millennium with statistical confidence? While I’ve spend more ink on Mann et al., I’ve also posted comments on all the other multiproxy studies. There are a couple of reasons for spending more time on Mann: first, after considerable effort, I’ve been able to winkle out a great deal of information on data and methods; I’m in an earlier stage of this quasi-litigation with other multiproxy authors. For example, so far, Briffa has not even identified the locations in his MXD study, Second, Mann is more widely used. Third, there has been considerable after-market efforts by Mann and his students to purportedly counter the criticisms and these responses also require after-market support.

There are a few issues with the bristlecones. First, one would expect a “robust” reconstruction to yield similar results without bristlecones. Indeed, Mann claims this. However, this is not the case: i.e. if you use ALL the other proxies in an MBH type reconstruction, you can’t draw any conclusions that the 20th century is statistically significantly warm. Second, Mann claimed that his results were robust to presence/absence of ALL dendroclimatic indicators; indeed Bunn et al specifically cited this claim. However, this is not true as it is not robust to bristlecones (which Mann knew). Mann withheld this adverse information and has misled successive readers, including Bunn. There was some veiled language in MBH99 that Mann sometimes uses to excuse the withholding but it is not a clear warning to readers and Mann et al 2000 re-iterated the original false claim about robustness anyway. Third, one would like to see updated information on bristlecones – is their growth off the charts in the warm 1990s? If not, how can we rely on earlier info as a temperature proxy? Hughes updated bristlecone information in 2002, but it is not used in Hughes and Funkhouser [2003]. My speculation is that the updated information will not show off-the-chart growth and that’s why Hughes is sitting on the results. People who follow mining promotions (as I’ve done) as really sensitive to delays in reporting results as promoters with bad results will delay erporting them hoping for some offsetting good results. The delay window for mining promoters is really short, but there seems to be no time obligation for paleoclimatologists. When is Thompson going to publish Puruogangri? Fourth, within ITRDB, the growth increase in high-altitude sites collected by Graybill is MUCH higher than a very slight growth increase in high-altitude sies collected by all other researchers. (I’ve not mentioned this before). Why is that? Fifth, in our E&E article, we discuss a number of nonclimatic or non-temperature factors that could affect high-altitude bristlecone growth other than CO2 fertilization. While CO2 fertilization needs to be eliminated by proponents of bristlecones as index, so does phosphate fertilization (possibly a factor in poor soils), so does the overall US Southwest woody plant growth spurt in response to 19th century sheep overgrazing if bristlecone growth is to be held out as a unique arbiter of world climate history. Sixth, altitude – medieval bristlecones were at higher elevations. Simplistically that speaks volumes to me. Dendrochronologists (other than Naurzbaev) seem over-determined to neglect changing altitudes – see the ridiculous commentary by Briffa et al in the 1996 NATO volume.

The dC13 paper is not very definitive at all. Plus, do you stand behind CO2 fertilization or not? Your having your cake and eating it too is tendentious. Don’t make me smoke you out again by mischaracterizing you.

That’s not how science works. You’re holding a gun to his head, much as JMS et al. does on GW: “we know it’s not solar forcing, volcanoes, or aerosols, so what else could it be other than GHGs?” When you don’t understand completely how a system works you must allow for the possibility of surprise. You must be agnostic. You must keep an open mind, and gather more data through systematic experimentation.

I’m holding a gun to his head because he wants to use tricks of rhetoric to have his cake and eat it too. I have no problem with him making limited statements. Just problems when he wants to act as if they aren’t. And I will call him on it every, every time.

Nitrogen, trace elements, nonlinear positive response to temperature, interactions … these are all valid alternatives to CO2 fertilization which have been discussed at various times and are not easily dismissed.

Ignoring #23, please explain what’s wrong with arguing a point from both directions simultaneously when the data are ambiguous? It’s not “having your cake and eating it too”. It’s dialectic. It’s conjecture and refutation. It’s Popper. It’s science. Maybe you want to go look that one up?

The touting of the NAS was an appeal to authority for rhetorical effect for support for STeve’s “side” with comments that he himself does not stand behind and from an authority that he KNOWS did little to justify it’s opinion. That sort of thing is not science. It’s debate games and lawyer silliness and it’s DISHONEST.

TCO, I think that it is entirely reasonable to rely on the NAS panel for some things and not for others. Same with Wahl and Ammann. I think that Wahl and Ammann, as an overall article, is profoundly unscientific, but it is quite reasonable to cite their calculations of verification r2 statistics as confirming and extending our results. By doing so, I am not obligated to agree with their conclusions that Mann’s errors do not “matter”.

Similarly for the NAS panel. It is quite reasonable to cite them as authority for the methodological proposition that strip-bark trees not be used – similar points had been made in IPCC 2AR and were surveyed in MM05(EE) and had been expressed by panelist Biondi in Biondi et al 1999 – without acquiescing in their sloppy recapitulation of even sloppier prior literature.

I’m not in a position to determine from first principles what caused anomalous bristlecone growth in the 20th century – whether it was CO2 fertilization or nitrate fertilization or sheep. All that is relevant at the multiproxy stage is that specialists state that the growth spurt was not caused by temperature. If the Team want to use this proxy, it’s their job to show its applicability in the face of these problems, not my job to solve the physiology of bristlecones.

1. Do they agree that it was not caused by temperature? I have not seen a synthesized argument on that from each expert. I have seen a collection of random posts and articles on possible confounding factors (dry-lakebed-blowing*, strippedness of bark, CO2*, sheep). Is it that panapoly of possible confounders that drives the doubt? Or is it just the simple issue of failure to correlate with gridcells? If it is just the simple non-correlation, then is all the other stuff just window-dressing to make it look like there are more independant faults then what there really are?

Note, that the litany of issues has not been provided in the context of comparison to other tree-ring species. Are the bcps WORSE then other trees as proxies? Or are you just picking on them, becuase you want to eliminate the “high end” and skew the average by leaving data out?

2. Citing an authority, who you know has not really looked at the problem is dishonest. It would be the same dishonesty if they had done an analysis that favored your point of view (and you cited it for support as an appeal to authority when you knew that they had made fundamental flaws in the analysis).

3. When we go to the further extent, that you use these same high faluting authorities who have done less thinking on the problem then you have (thus not justifying their statements) and then use their firm sounding pronouncements, while yourself not willing to stand behind them, but willing to use them for your rhetorical device)…well, that’s dishonest in another way.

4. You’ve done a great service by exposing some of the tricks that Mann et al used to argue a point rather then to reveal nature. But when you play these rhetorical games yourself (to help your “side”, while confusing rather then illuminating issues), that is wrong.

* And for example when we look at the dC13 article it is not very solid support. Does not remove temp as a confounding factor. That dC13 article in the context of this discussion is just more “dry-lakebed” thrown against the wall to see if it sticks.

TCO — As I understand it, the bristlecones were originally chosen for study precisely because their recent growth did not correlate well with the local temperatures. The researchers were looking for examples of such trees because they were interested in testing a theory about a particular non-temperature effect (CO2 fertilization) on tree growth. Whether or not their explanation for the non-temperature effect is valid, the fact remains that this particular set of tree ring data does not correlate well with local temperature. Knowing that, it was unreasonable for the original researchers to use the series as a temperature signal, and dishonest to continue to use them, and say they didn’t matter, when they knew that the reconstruction fell apart when these particular outlier series were removed from the data (the CENSORED directory). It remains an open and interesting scientific issue of what these trees are responding to, but the lack of correlation of their recent growth with local temperatures is what kills off the hypothesis that their recent growth spurt reflects temperature. Just because one cannot be definitive about what the alternative explanation for recent growth is does not imply that it could be temperature. The evidence for the position that temperature is not relevant is direct.

Lamarche et al 1984; Graybill and Idso 1993; Biondi et al 1999. TCO – in fairness to your point on citing the NAS panel, I agree that the NAS panel saying something doesn;t make it so; the issue is that reasonable proxy selection protocols for temperature proxies require them to be temperature proxies and not contaminated by nonclimatic fertilization and that there is specialist doubt about whether the bristlecone growth in the 20th century is due to tmepreature, most recently expressed by the NAS panel.

Look, the arguments about bristlecones that we made in MM05b have NEVER been responded to or acknowledged in any reply to our publications – be it by Mann, Wahl and Ammann, von Storch and Zorita, Huybers, Burger and Cubasch – they all say that it is a problem for “another day”. realclimate avoids bristlecones like the plague. I’d be happy to parse bristlecone botany if any of them step up to the plate, but I don’t really have much to add to MM05b. Is there anything in there about bristlecones that you object to?

I need to reread it, but first guess would be lack of comparison to other tree rings to show that bcps are “more flawed” then “regular tree rings”. I also think that an overall, objective look at the issue is a task in and of itself. Doubt that your comments are overarching on the subject. Suspect that you picked what you had to fit in with your overall argument.

I also hate the publication in EE. (It’s not part of normal scitation search referenced publications.) Why not, publish a review article on bcps in Dendrochronologica or Journal of the Tree Ring Society or whatever? If you’ve really well covered the ground, then it should be a simple cut and paste (and still worth it). I suspect when you go to attempt this, you will find that your comments within that article are not sufficient for a fair assessment, are more of an argument (citing only the things that “help you”, rather then surveying the whole issue fairly).

TCO, you are hopeless. If the reconstructions are not robust to deleting the bristlecones, they are not robust. Period. If they have to depend on one or two series which even MAY be influenced by a non-temperature variable, then there is little probability that they are meaningful. Why do we care if they are “more flawed?”

I think we need to go back an think about exactly why BCPs were considered as a candidate for a temperature proxy at all; as opposed to, say, sugar maples in Vermont. The whole idea of tree-ring temperature proxies is to find species growing at the timber line where precipitation isn’t the limiting factor (within the range of temperatures under consideration). Growing there means you’ll have sparce stands so you don’t have to worry about crowding as a factor. Being in moist areas means the temperature signal isn’t confused by changes in precipitation.

But, as Steve has shown, there are local weather stations which show that the “temperature signal” doesn’t correspond to the local temperature. Therefore, if this signal is to be of use, it must tele-correspond to global temperatures via some mechanism or other. But the only ones I can think of must be precipitation proxies. And this then collides with the very reason for chosing BCPs in the first place. Therefore any attempt to claim, as Mann has, that not using them would be throwing away valid signals is seen as just plain wrong. Either the multiproxy reconstructions should be robust to the absence of BCPs or they should be thrown out.

Re #34-36
This is where TCO’s argument in #34 and elsewhere is just. A comprehensive study of BCP ecophysiology & ecology is badly needed. If Steve M chooses to spend his time writing a book about the big picture issues (which are of obvious importance) this would take the flame out from under the feet of those who want to keep using the BCPs, business as usual. TCO wants more concrete proof, whether (+) or (-), of BCPs worth as a proxy.

#37. It would be nice if the Guelph cedar specialists – Kelly, Larson,…– spent some time on bristlecones and did exactly that. They’re well qualified to do so; I’m not. My point remains: BCPs should be out until someone proves that they can be re-qualified. You have IPCC 2AR, the NAS Panel, Graybill and Idso, Hughes and Funkhouser, Lamarche et al (including Fritts), Biondi et al. What do you have in favor – Wahl and Ammann? C’mon.

If you’re not “qualified to do so” then how is EE05 supposed to “have done so”? I guess you are conceding my point in terms of a fair overview of bcps, not having been performed.

You still have not responded to my point about the need for comparative norming. Are the bcps especially bad? Has it been proven? When you avoid a point like this it makes me suspiocious. Reminds me of how you did not answer my question on “is PC1 the same thing as the ‘hockey stick'” in 2005.

On a humerous note: you left out Rob Wilson’s “they’re not so bad” support of the bcps in the esteemed journal Climatica Auditica. :)

#40. TCO, I can’t respond to every comment on this board and still do anything else. In MM05 (EE), we thoroughly reviewed the botanical literature on bristlecones – something that Mann should have done if he was relying on bristlecones and did not do. To do a study of bristlecone physioology from bottom up is a big job and one for botanists.

Are they “especially” bad? There’s no need to undertake a beauty contest. The relevant specialists said that they should not be used. My own experiments comparing gridcell and local temperatures to growth show no relation. What else do you need?

1. I know that you can’t respond to everything and that I tend to have multiple non-trivial essay questions buried at times in my style of posting. That said, my impression is that if I ask a question that highlights something that helps your cause, you are more likely to address it then if it is the converse, even if the importance of the question is equal. The PC1/reconstruction thing could have been answered in less then ten words: “The PC1 is NOT the hockey stick graph.” Just let the chips fall!

If you wanted a longer discussion, it could have been:

The PC1 is not the same thing as the “hockey stick” or the overall reconstruction. It is an intermediate result that feeds into the hockey stick graph. The “impact of mining” on the PC1 is larger then the “impact of mining” on the hockey stick itself, so that questions about impact of mining on the hockey stick should not be answered with PC1-based results as that would be an overstatement of impact. There is some relevance to discussion of the PC1 itself, based on a figure and some text in MBH that discussed MBH.

I suspect that your reluctance to find the time to clarify the issue had to do with the difficulty in keeping the picture looking as bad for Mann, if you supplied the “simple sentence” answer to my question. That you allowed or promoted confusion on this issue is troubling to me. Do you think jae or ‘rocks or JohnA are walking away with a fair picture when you allow/promote such confusion?

2. I’m still not getting you. You’re saying that EE05 covered things fine, but when pushed seem to imply that a good review of the situation is lacking and you are incapable of providing it.

3. The reason for the relevance of comparison of bcps to general tree rings is rock simple, Steve. It doesn’t take a “coulda been a Fields Medalist” mind to follow this. :) The question is are the bcps some especially bad part of the data set, which one is justified in removing? Or are you just finding fault with the data points that it helps your cause to find fault with? If the rest of the data set is as ugly as the bcp (has as low of a correlation to gridcell temp…if that’s your guage, has as many significant confounding factors), then the analysis develoves to a simple statement of the general issues with tree ring proxies and the bcp-specific kerfuffle is irrelevant.

If the bcps show no correlation to local temperature, then they should be thrown out for that reason alone. The details about all the other tree series used in the reconstructions don’t matter, since they apparently don’t show any significant trends one way or another. I’ve been saying for over a year that these guys should not be using trees as thermometers without FIRST showing that this is feasible. If it were feasible, you would think that someone would have demonstrated it by now. The basic science is apparently missing.

Why should you throw out the trending data rather then throw it all out (trending, non-trending) if it suffers from the same issue. If the trending data suffers worse then the non-trending data, then show that.

It is of course, a conceptual point. An idealized upper treeline tree would respond only to temp and an idealized lower treeline one only to moisture. Obviously the real picture is one of the upper responding “more” to temp and the lower “more” to moisture. The question is how much is “more” and how does “non-idealness” affect specific inferences made on larger sets of proxy data. I can imagine cases where the idealization is irrelevant and one can’t use the proxies at all. Can imagine other cases, where the lack of ideality is irrelevant to broader inferences (with enough data, with independance of input variable variation). Of course, I would really like to see some multiple regressions over the input variables. The Finnish articles were quite nice in that respect. Don’t recall the equivalent for BCPs.

For that matter, how do temp and precip vary themselves in this part of the world? Are the dependant, inversely dependant or independant?

So–you pick trees on a very arid site (cactus zone, no less!), where you have good apriori reasons to believe that precipitation would be THE limiting factor, and then you try to justify using them for thermometers. This is simply laughable. Another reason to ignore the bcps. And just because a tree grows near treeline does not indicate that there is “plenty of moisture available.” Many treeline areas have extremely shallow and/or sandy soil, which can cause all sorts of moisture stress. I just don’t think we can hope to discover what was controlling tree growth rates at a given location even 200 years ago, let alone 1000 years ago.

In fact, Fritts studied bristlecone growth in detail in 1969 and reported that growth was controlled by moisture stress – we discussed this in MM05 (EE). The link to CO2 fertilization (And Fritts was a coauthor of Lamarche et al 1984) is that CO2 fertilization supposedly enables more efficient use of moisture. It is unbelievably absurd that this is still being debated and that the NAS panel did not move off its butts to perform any due diligence on the “other” series in their spaghetti diagram.

RE 46, TCO, you make some excellent points, including inquiring into the relationship between temperature and mosture. However, you say:

An idealized upper treeline tree would respond only to temp and an idealized lower treeline one only to moisture.

I don’t think this is true. Growth for trees is neither a function of temperature alone nor of moisture alone. Growth is some function f(T,M) that takes into account whether the temperature is higher than can be sustained given the available moisture. If a tree has plenty of moisture, it can cool itself through evapo-transpiration. If it doesn’t, it heats up and growth slows or stops.

The upper treeline is where the moisture and temperature (plus other stressors including reduced CO2, decreased atmospheric pressure, and increased UV) are such that the trees can not live any higher. Even a theoretical upper treeline, however, is not necessarily “temperature limited” by low temperatures. High regions are often quite arid, and steep hillside slopes hold water poorly. Thus, the problem often is that although the temperature is warm enough, there simply isn’t enough water during the growing season for the trees to grow.

Having lived near the treeline as a kid, I remember seeing this many days during the summer. The treeline trees would be plenty warm, and in the morning they would be growing. But in the afternoon, they would droop, lose turgor, and stop growing as the temperature outpaced the available water. The limitation was not temperature “¢’¬? it was water.

Finally, even a theoretical upper treeline needs to recognize the other stressors listed above.

Thanks, bender. Willis, in the ideal situation moisture is present in excess at starting temp and is still in excess at the higher temp.

Steve, you’ve said that before. So? Are you arguing that all bcps are always moisture starved? What about the cactus? Isn’t it possible that it could occasionally be in a situation where precip is in excess and temp is the limiter? The only thing interesting in your statement, is if you want to make the argument that the lower boundary is related to soil, not to precip so that precip studies (lower treeline) might not be so valid…

Just that the type species for world temperature should not be trees in an extremely arid climate competing with cactus, on extremely poor soils with known botanical fertilization trends – what’s so hard to understand about that?

To claim in any capacity that this science is fully understood or settled enough to determine global temperature so exact as fractions of C over large time scales (as the HS or the UN or any other study using them seems to pronounce) and to want make social policy from it is mind boggling to many of us (scientists included!)

And if you can google and get 12,200 hits for “problems with using tree rings to define temperatures”. and just read a few abstracts…sheesh, I know what that tells this nobody like me and I don’t like it one bit.

(This first one mentions Mann et al)

Reichert et al.: A FORWARD MODELING APPROACH TO
PALEOCLIMATIC INTERPRETATION OF TREE-RING DATA
submitted to J. Climate
3/24/2004 http://ic.ltrr.arizona.edu/pp/reichert2004.pdf
ABSTRACT
We investigate the interpretation of tree-ring data using the Vaganov-Shashkin forward model of tree-ring width formation. This model is derived from first principles of the biophysical ecology of conifer trees, and explicitly incorporates a nonlinear daily-timescale model of the multivariate environmental controls on tree-ring width over the growing season. As measured by the fit to actual tree-ring observations, we find that the daily-timescale meteorological inputs, and the non-linearity of the modeled growth response, are important determinants of model skill. The model results are shown to be robust with respect to primary moisture and temperature parameter choices. When applied to the simulation of tree-ring data from North America and Russia from the Mann et al. (1998) and Vaganov et al. (2004) data sets, the forward model produces skill on annual and decadal timescales which is equal or better than that achieved using classical linear statistical modeling. The results suggest future model application to the -development of improved proxy error estimates and climate reconstructions, and the -prediction of the fingerprint of transient climate change on temperate conifer forests

A quantitative analysis of the interactions
between climatic response and intraspecific
competition in European beech
E. Piutti and A. Cescatti
Abstract: In dendroclimatology, trees growing at low competition level are often sampled, to avoid the effects of competition
on tree growth. But trees generally live in dense stands, and the analysis of the climatic response should take into
consideration the intraspecific relations, because competition could affect resource availability and climate sensitivity. To analyze the climate competition interactions…

Some conclusions from this study “Millennia-long tree-ring chronologies
as records of climate variability
in Finland” Samuli Helama
Division of Geology and Palaeontology
Department of Geology
P. O. Box 64
FIN-00014 University of Helsinki, Finland:

…
7) Both of tree-ring based palaeoclimate reconstructions provided evidence for greatly fluctuating Holocene climate. Apart from volcanic impact, potential climatic forcings, driving the temperature or precipitation variability, were not examined here but this part of the research remained to be tested later. This can be done using for example frequency, correlation and regression analyses.

8) Whereas the 20 th century experienced relatively warm summer-time climates in the context of the past one thousand years, the coldness during the 19th century was perhaps the severest of centennial periods during the past millennium. On the otherhand, there were indications that the 16th
century was in overall warmer than the 20th century. Towards the end of the past century summer temperatures did not
seem to be rising.http://tinyurl.com/mko3z

#57. TCO, but then somebody has to demonstrate it and it should have been done prior to introducing these series into the temperature reconstructions in the face of specialist opinion to the contrary. If there were such a demonstration hanging around, you can bet your boots that the Team would have put it into play by now. The silence of the Team on bristlecones is a dog that isn’t barking.

Ok, I looked at the table. The “looking at different seasons” is similar to the work done by some of the Finns on their tree series where they even do month by month examinations. They give a botanical explanation of the effects they see, (spring, winter temp effects). With respect to that, I think a formal multiple regression would be better. If they think that spring temps are negative because of drought, then an analysis the removes the confounding effect of said drought should be performed multiple regression).

The summer temp effects are low and not statistically significant. I’m not sure what Mann used in his temp plots (was it summer or was it year round)?

My stats gaps will show here, but I’m not clear what the higher Pearson correlations means intuitively for the issue at hand. Is the variability of the forcer included? (Is it normalized by std deviation?) For instance, if r for PDSI is heavier then r for temp, but temp variaion is much more then PDSI, then the tree would still be an effective tree in the sense of limiting stand, no?

I’m a little concerned with the number of variables examined (15 for each species). Also, would like it if they came up with some sort of equation at the end (maybe using Akaike criteria) for what they think a reasonable growth predictor is for the trees.

Finally, I might be missing it, but I don’t see any botanical (physical) rational for why strip bark behaves differently wrt CO2 then full bark. Is it intuitively correct to think of strip bark trees as “half dead”? How does said condition make the tree better able to utilize additional CO2?

I don’t see any botanical (physical) rational for why strip bark behaves differently wrt CO2 then full bark. Is it intuitively correct to think of strip bark trees as “half dead”? How does said condition make the tree better able to utilize additional CO2?

I could be totally backwards, but I think the reason is that generally strip bark trees have a greater root system per width of bark. We know that these trees are limited by many things including temperature, moisture & growth factors (CO2, minerals, etc.) So a largish root system will be able to gather more minerals. Meanwhile more CO2 in the atmosphere will both let the trees (at times when temperature is high enough for photosynthesis), gather more CO2 and less moisture will be lost in the process. The net result is synergistic and a full bark tree, while it will have greater total production, will be limited for minerals and thus the ring widths will less than a strip-bark tree where there are plenty of minerals available.

You’ll recall that young trees generally have wider ring widths and this is basically for the same reason. The roots systems can spread out in a circle (or even sphere) without having to worry about “competition” from roots from other parts of the tree.

Re #71
I think it’s the opposite. Strip-bark trees have a greater portion of the root system dead. Root systems are a sink for CO2, so if you remove half that sink, you make alot more available for allocation to above-ground growth. Dano will correct us if we’re wrong.

Dano can only correct us if a study has been done of root area/mass for strip bark trees. Sounds like a rather complicated study to do to me, so it’s problematic if its been performed or not.

Hmmm. I’d suggest something like injecting a radioactive isotope of a mineral (in solution) into the ground in localized areas in some sort of grid system and then seeing how much appears at time X in the needles. If you have a short enough halflife you might be able to do the various areas sequentially. Or if it’s penetrating radiation (i.e. a gamma emitter) you might be able to trace the root systems assuming they’re relatively shallow.

Re #71
G&I were putting several independent, and to some degree alternative, mechanisms on the table. #71 was one of them. #72 was another. In retrospect I’d say #71 makes a lot of sense. #72 seems more speculative & unlikely.

The net result is synergistic

This is a critically important proposition – because the reconstructionists use additive models, not synergistic models. Furthermore, I suspect it is a correct proposition.

Re #77
1. On synergy. Credit where credit is due: you said it here first! (I’m a mere co-discoverer.) Well done.
2. On leaving out C. I did that on purpose, because that’s what Salzer & Kipfmueller (2005) do!

My 2 cents worth. I went to my undergraduate geologic field camp in the southern White mountains, Cerro Gordo peak and adjacent areas. Very dry thats for sure. I am wondering if possibly human influence in the valley bottoms might have an indirect effect on the trees growing at altitude? Before say 1890, the Owens valley (just west of the area in question) had a significant river running through it, which filled Owens Lake. After the late 1890’s to early 1900’s (correct me if my timing is slightly off, its been many years)the water from that river was diverted to the Los Angeles basin. What once had been a lake dozens of feet deep year round is noting more than a giant dust bowl today, this is the area just south and east of Lone Pine Calif. But the point and effect have travelled all the way north into Mono Lake near Mammoth. Water that once naturally moved through the valley is now mostly transfered to the LA/So Cal area.

So, the question is, will that effect growth rates in the trees at altitude that are used for the studies mentioned in this blog? I don’t know, but it seems like it might have some effect. Seems like it might slightly change the valleys climate/air moisture content, and in such a dry place, doesn’t every drop of water count in plant/tree survival? Would this possibly bias the studies in some way?

Two major uncertainties lie in the statistical development, analysis and interpretation of tree-ring data for paleoclimate studies. First, there are nonclimatic influences on tree-ring records, including tree biology, size, age and the effects of localized forest dynamics [Cook and Kairiukstis, 1990].

Perhaps of more concern is that tree ring data reflect a nonlinear response to multivariate climate forcings.

Read the whole paper for context. This shows the dendros are working on the problem.

What’s your take on this from 5.3. Implications for Statistical Paleoclimatology?

…in a majority of the tree-ring width chronologies studied here, the decadal variability was not skillfully resolved at or above the 90% level of significance by either modeling approach. This suggests that much of the decadal-scale variability evident in the tree-ring width data may not be directly related to decadal-scale climate variations.

Mine is that there isn’t a relationship between their studied tree-ring width data and decadal-scale climate variations and both modeling approaches were found wanting.

First, there are nonclimatic influences
on tree-ring records, including tree biology, size, age and
the effects of localized forest dynamics [Cook and
Kairiukstis, 1990]. Successful elimination of these influen-
ces is now routinely achieved via careful site selection,
sampling, data analysis and a posteriori tests to ensure that
the tree-ring record is dominated by the single climate
variable of interest.

I’ll look on my own, of course, but any link to exactly *how* these influences are routinely eliminated would be welcome.

I needed to comment somewhere after reading various websites and papers on dendrochronology, PCA analysis and the like and its impacts
on climate predictions. I read the Mann paper and a few others from the realclimate site and links. Interesting.
I’m a physicist and mathematician and my major objection to the use of proxy data is that there is a lot of statistical analysis without
understanding the relationship between tree growth, species of tree, water, temperature, Co2 etc. Where can I find the equations
showing how a tree ring is formed in a certain atmospheric concentration of Co2 and water at a given temperature?
PCA analysis is a good tool if you already know the form of the underlying relationships. otherwise immediately you are assuming a
linear relationship between variables and more importantly this isn’t being stated as an assumption (i.e. rule no 1 in scientific
method). I understand it requires lots of work to get the underlying functions
but it seems that some biologists (is this the proper word for dendros) are using the
tools without understanding them and then standing back and saying ‘but look there’s a correlation’.
That’s misrepresenting the truth and the method. Science isn’t tough to do but you have to do it properly.

#84. There obviously is no such equation relating ring widths to underlying conditions. There is a tremendous variation between sites and a natural temptation for dendrochronologists to ex post pick chronologies that fit their world view. Unfortunately this habit is deeply ingrained in dendros and even as thoughtful a dendro as Rob Wilson challenges what seems to be an elementary point.

This has been an interesting read, but I suggest a simpler engineering approach: It is obvious that the Dendros are still developing their methods, and cannot yet agree on much. (and the CO2 church will defend anything that can be “scientifically” refuted) Consequently, although very interesting, it is probably futile to argue about the conflicting details in the dendro industry.
On the other hand, MBH99 has a simple GLARING ISSUE in that the proxy data is discontinued in 1980. The problem is, that if it is OK to use tree-ring data to infer millenial past temperatures, then it should also be OK to take it for the full period under review. Unfortunately, MBH99 prefers, to “illegally” stop short and create an impression of ballistically upward trend stopping with the totally different/irrelevant instrumental global average high spike back in 1998. However, if the red data is removed from the graph, the remaining blue proxy data is clearly showing an unresolved substantial down-trend over 3 decades versus a larger up-trend on T. (That is without considering any CO2 response etc, which would seem to make the contradiction even worse)
OK…what does later proxy data suggest…Briffa 2000 managed to take it to the full period of review, and there is a 50 year mean downtrend from 1950….Oh dear! I remember a paper by Jan Esper from about 2000 in which he is clearly distressed by sustained opposing trends between “recent” growth rates and T, but it seems to have been removed from his massive list of publications
Has anyone seen anything to contradict an apparent major divergence of 5 decades or more?
Why has the IPCC dropped MBH99 in the 4AR 2007?
Should policy makers and media be carefully advised?

There is a host of literature around on dendro-archeology. Holland just got a first professor who is also a prized poet. Check for prof. Esther Jansma, professor of dendrochronology and paleo-ecology of the Quarternary at
Utrecht university.